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Hello! When the access resistance of R2 is the smallest, that is, 0, the resistance in the whole circuit is the smallest, and only R1 is connected to the circuit at this time, and the current is the largest.

Therefore, the voltage across R1 is U1 IR1

At this time, the R1 voltage is equal to the power supply voltage, the power supply voltage U=12V, when the R2 resistance value is adjusted to the maximum, the circuit resistance is the maximum, at this time, the minimum circuit current is R1 and R2 in series, the voltage of R1 is U1 IR1 R2 The voltage of R2 is U2 U1 12 4 8VR2 The resistance value is R2 U2 I 8 0 2 40 ohms.

Therefore, the maximum resistance of R2 is 40 ohms.

According to the power formula p=i 2r1

When the current is smallest, the resistive electrical power is the smallest, which is P1 i 2R1 0 2 0 2 20 0 8W

When the current is maximum, the resistive electric power is the largest, which is P1 I 2R1 0 6 0 6 20 7 2W Wang.

1，i=u/(r1+r2)

The total current is the smallest, and the R2 resistance is the largest.

The total current is maximum, and the R2 resistance is minimum=0

United. u=12v

r2 = 40 ohms.

2，p1=i^2*r1=

p1'=i'^2*r1=

P1 ranges from tile to tile.

The first question is that if the internal resistance of the ammeter a is not considered, then r2=40 can be solved by u=. If the ammeter has internal resistance Ra, then this resistance is connected in series with R1 and R2 to meet U=, no matter what the value of Ra, the R2>40 is sought, but I estimate that this factor is not considered in the question, and the "maximum resistance" of R2 is 40. The second question is that regardless of whether the internal resistance of the ammeter is considered or not, the power of R1 can be found by the formula P1=R1*I 2, since the range of change of current i is, then the range of power is.

When i=, only r1 is connected to the circuit, you can find u=12v, when i=is, r1 and r2 are connected in series in the circuit, you can find the total resistance of 12 ohms, and subtract the resistance of r1 to get r2=40 ohms.

The transformation range of power is solved by p=ui, p1=12*, p2=12*(1 3)*

The next sentence is not as good as a famous teacher to guide the way.

Original sentence: It is better to read 10,000 books than to travel 10,000 miles; It is better to travel thousands of miles than to read countless people; Reading countless people, it is better for a famous teacher to point to Shi Minlu, and a famous teacher to guide the way is better to understand it yourself.

The source is: Ming Dynasty, Dong Qichang's "Painting Zen Room Essays - Volume Na Cover II" has "The people of the past commented on the New Year's paintings, and they said that they had ten thousand books in their chests." What's more strange, and the big year to the clan is not allowed to travel, every dynasty back to the mausoleum, you have to write the hills and ravines in the chest, not thousands of miles, do not read thousands of books, want to paint the ancestors, it can be a branch of the eggplant? ”

Hello, reading countless people is not as good as a famous teacher to guide the way.

The complete sentence is a sellout: it is better to read 10,000 books than to travel 10,000 miles; It is better to travel thousands of miles than to read countless people; Reading countless brothers, it is better to have a famous teacher to guide the way, and a famous teacher to guide the way is not as good as to understand the envy and be wide by yourself.

The Turtle and the Eagle: Ambitious, unrealistic, and bound to fail.

Ants and cicadas: People who indulge in indulgence often have sad results.

Camels and Zeus: Man cannot be insatiable.

Two pockets: People tend to find fault with the shortcomings of others and ignore their own.

Donkeys and wolves: restless and self-sufficient, often suffering misfortune.

Horses and donkeys: People should help each other.

The fox and the hungry dog: **'s tricks will always see through.

The Dog: One cannot be greedy.

Mosquitoes and lions: Even if a person has achieved great success, he must not be blindly complacent, because pride can lead to negligence and often lead to failure in a small matter.

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